EP1478828B1 - Recirculation structure for turbo chargers - Google Patents

Abstract

Recirculation structure for turbocompressors, having a ring chamber which is arranged in the area of the free blade ends of a blade ring largely upstream of the latter and adjoins the main flow duct. A plurality of guiding elements are arranged in the ring chamber distributed over its circumference and are arranged and shaped in a fluidically advantageous manner with respect to the recirculation flow, with recesses provided in the leading and/or trailing area of the ring chamber. The side of the ring chamber which adjoins the contour of the main flow duct is open along its axial length as well as along its entire circumference, the free edges of the guiding elements being situated on the or close to the contour of the main flow duct.

Description

The invention relates to a recirculation structure for turbocompressors, according to the preamble of claim 1, as well as an aircraft engine and a stationary gas turbine.

Recirculation structures for turbocompressors have been known for some time and are generally referred to in the art as "casing treatments". These have primarily the task of increasing the aerodynamically stable operating range of the compressor, the so-called surge limit to higher compressor pressures, i. to a higher compressor load, is postponed. The faults responsible for a local stall and ultimately for pumping the compressor occur on the housing side at the blade ends of one or more compressor stages, on the hub side on the radially inner guide blade ends, since in these areas the aerodynamic load is highest. The flow in the area of the blade ends is stabilized again by recirculation of the "air particles" circulating between the blade tips with blade speed and having a reduced energy into the main flow with an increase in energy. Since flow disturbances usually do not occur uniformly over the step circumference, a compensation in the circumferential direction, in addition to the essentially axial recirculation, should also be possible. The main disadvantage of the known "casing treatments" is that while they increase the surge limit, they reduce the compressor efficiency on the same side.

DE 33 22 295 C3 protects an axial fan with a generic "casing treatment". One recognizes there an annular chamber (8), in the guide elements (9) are fixedly arranged. In the downstream area above the blade ends there is a circumferentially open area into which the vanes do not extend. A characteristic feature of this type of "casing treatment" is a closed ring (7) which is aligned approximately with the contour of the main flow channel and separates the rear inlet area from the front outlet area of the recirculation structure and forms a smooth, closed surface area.

A very similar "casing treatment" is known from DE 35 39 604 C1, wherein here in the front and rear of the annular chamber (7) an open area in the circumferential direction is present. Note also here the radially inner ring. 6

A newer "Casing Treatment" is known from US 5,282,718 A. Here, the annular chamber (18, 28) and the guide elements (24) are fluidly refined. Here, too, inlet and outlet of the recirculation flow are separated by a solid ring which is smooth and closed towards the blades. Such rings in the blade area must be provided in the event of contact with the blade tips usually with a Anstreif- or inlet lining.

There are other "Casing Treatments" with axial or axial oblique grooves, such. disclosed in US 5,137,419 A. These are therefore not considered here, since lack of connection of the grooves with each other in these versions no flow compensation in the circumferential direction is possible.

Document US 3,620,640 A protects a shroud with a recirculation structure for a propeller or fan. The recirculation structure comprises a ring chamber (toroidal cavity 2) which is circular in cross-section and in which profiled partitions 5 can be arranged. The adjacent to the main flow channel side of the annular chamber (2) is open over its axial length and over its circumference to the main flow channel. As particularly shown in Figures 2 and 3, the axial center of the annular chamber (2) coincides relatively accurately with the axial center of the propeller blades (propeller blades 3) with the open side of the annular chamber extending upstream and downstream of the blades (3).
The guide elements (5) reach only at their downstream, rear end to the contour of the main flow channel, ie to the inner contour of the shell (shroud 1), zoom. In the upstream direction, the free edges of the guide elements (5) more and more away from the main flow channel and the blade tips (see the forward obliquely rising edge profile of the guide elements (5) in Fig. 2 and 3).

Document US 5,474,417 A relates to a casing treatment for compressor blades in which the annular chamber is substantially closed to the main flow channel and has only one discharge slot at the upstream and downstream ends. See the annular, the annular chamber largely occlusive element 46 which is provided with an inlet lining 72.

In view of the disadvantages of the prior art solutions, the object of the invention is to provide a recirculation structure for turbocompressors, which allows a significant increase in the surge line and thus a significant increase in the stable operating range without relevant deterioration of the compressor efficiency.

This object is achieved by the features characterized in claim 1 features, in conjunction with the generic features in the preamble.

The essence of the invention is that the annular chamber, which is completely open to the main flow channel over its axial length and circumference, lies with its axial center upstream of the axial center of the free blade end, and that the free edges of the guide elements are at or near their axial length lie the contour of the main flow channel. Ring-like elements with squish coverings, etc. omitted. The abovementioned patents show that experts have hitherto attempted to carry out recirculation structures to the main flow channel, ie to the so-called annular space over as large an axial area as possible, with little gap and closed, in order to maximize flow-favorable and low-loss extension of the contour of the

Effect main flow channel. In contrast, the invention leads to gaps, rugged surfaces, etc., and thus appears to be disadvantageous and inappropriate. Experiments have shown, however, that the recirculation structure according to the invention is superior to known solutions both in terms of surge limit and in terms of efficiency. This is aerodynamically explained by the fact that the free, casual formation of the recirculation flow in the open annular chamber with freestanding vanes and flow connections in the circumferential direction is more important than a possible gap-free extension of the contour of the main flow channel. The lack of a closed ring has the further advantages that no squelch or inlet lining for the guide elements is required and radial space and weight is saved, resulting in structural mechanical advantages.

In the subclaims preferred embodiments of the recirculation structure are characterized according to the main claim.

• Figur 1 einen Teillängsschnitt durch einen Verdichter in Axialbauart im Bereich einer gehäuseseitigen Rezirkulationsstruktur,
• Figur 2 einen vergleichbaren Teillängsschnitt im Bereich einer nabenseitigen Rezirkulationsstruktur,
• Figur 3 einen Teilquerschnitt durch die Rezirkulationsstruktur gemäß Figur 1,
• Figur 4 eine Teilansicht der Rezirkulationsstruktur gemäß Figur 1 und 3 radial von Innen,
• Figur 5 einen Teillängsschnitt im Bereich einer gehäuseseitigen, gegenüber Figur 1 modifizierten Rezirkulationsstruktur, und
• Figur 6 einen Teillängsschnitt im Bereich einer gehäuseseitigen, gegenüber Figur 1 und Figur 5 modifizierten Rezirkulationsstruktur.

The invention will be explained in more detail with reference to drawings. In a simplified, not to scale representation:

• 1 shows a partial longitudinal section through a compressor in axial design in the region of a housing-side recirculation structure,
• FIG. 2 shows a comparable partial longitudinal section in the region of a hub-side recirculation structure,
• FIG. 3 shows a partial cross section through the recirculation structure according to FIG. 1,
• FIG. 4 shows a partial view of the recirculation structure according to FIGS. 1 and 3 radially from the inside,
• FIG. 5 shows a partial longitudinal section in the region of a housing-side recirculation structure modified with respect to FIG
• 6 shows a partial longitudinal section in the region of a housing-side, with respect to Figure 1 and Figure 5 modified recirculation structure.

The recirculation structure 1 according to FIG. 1 is integrated into the housing 5 of a turbocompressor and thus to be referred to as a "casing treatment". The flow direction in the bladed main flow channel 9 is indicated on the left with an arrow, so it runs from left to right. The flow strikes in the area shown first on a vane ring 13, then on a blade ring 20 and finally back on a vane ring 14. The radially outer contour 11 of the main flow channel 9 corresponds to the inner contour of the housing 5 and is to illustrate the left and right of the actual representation continued with dot-dash lines. The static recirculation structure 1 cooperates with the blade ring 20 and is located largely axially before this, ie upstream. The ring chamber 29, which forms the recirculation structure 1 together with the guide elements 37, adjoins the main flow channel 9 radially from the outside and is open towards the latter. The free edges 41 of the guide elements 37 lie on or close to the contour 11 of the main flow channel 9, ie they are at least approximately aligned with the housing inner contour. The guide elements 37 may consist of a metal, such as a Ni-based alloy, or of a light metal, such as Al, or of a plastic, such as thermoplastics, thermosets or elastomers. The front wall 33 and the rear wall 34 of the annular chamber 29 are inclined forwardly from their radially inner edges 35, 36 to be flow-favorable for the recirculation indicated by a small arrow.

The angle of inclination of the front wall is denoted by α, it may be the same or different in relation to the angle of the rear wall 34. Between the front wall 33, the guide elements 37 and the rear wall 34 recesses 45, 46 are provided which allow flow processes within the annular chamber in the circumferential direction, in addition to the predominantly axially extending recirculation. With 25, the free blade ends of the blade ring 20 are designated, in the area flow disturbances most likely to occur.

In contrast to FIG. 1, FIG. 2 shows a recirculation structure 2 integrated in a rotating hub 8. From left to right, a blade ring 21, a vane ring 15 with radially inner, free blade ends 26 and a blade ring 22 are identified in the main flow channel 10 Arrangement of a recirculation structure would consequently be referred to as "stroke treatment". The recirculation structure consisting of annular chamber 30 and guide elements 38 2 with front and rear recesses 47, 48 cooperates with a largely downstream vane ring 15. Since the "Hub Treatment" rotates here and the vane ring 15 is stationary, the rotor speed fully acts as a differential speed. The mode of action differs in principle not from that of a "Casing Treatments" In a turbo compressor, "Casing Treatment" and "Hub Treatment" can also be combined and used in several stages. The radially inner contour 12 of the main flow passage corresponds here to the outer contour of the hub 8.

FIG. 3 shows in cross-section a detail from FIG. 1. The guide elements 37 are inclined at an angle β to the radial such that the blade ends 25 of the rotor blade ring 20 convey the recirculation flow into the annular chamber 29 without major losses, the direction of rotation (see arrow). is to be noted. The angle of inclination β can decrease from radially inward to outward to the value "zero" given correspondingly curved guide elements.

A radial arrangement of the vanes, i. β = 0 ° is possible, but should be less aerodynamic.

The view according to Figure 4 to Figure 3 shows the blade profile of the blade ring 20 in conjunction with its direction of rotation (arrow) and gives a good idea of the flow-favorable profiling and curvature of the guide elements 37. The skilled person can recognize that the recirculation outlet in the upstream Edge 35 of the annular chamber 29 in relation to the blade ring 20 should be done here with counter-rotation. At 36, the downstream edge of the annular chamber is designated. It should be remembered that the guide elements 37 in simpler embodiments may also consist of flat or curved "sheets".

The recirculation structure 3 according to FIG. 5 is a "casing treatment" with an annular chamber 31 integrated in a housing 6. The guide elements 39 extend as far as the front wall of the annular chamber 31, recesses 49 are present in the rear area, in the immediate vicinity of the blade ends 27 of FIG Blade ring 23.

The free edges 43 of the guide elements 39 do not extend into the rotation range of the blade ends 27. Reference numbers 16 and 17 denote vane rings.

The recirculation structure 4 in FIG. 6 with annular chamber 32 and guide elements 40 is likewise a "casing treatment", which is integrated in a housing 7 and cooperates with a rotor blade rim 24. In contrast to Figure 5 rich here the guide elements 40 to the rear wall of the annular chamber 32. Recesses 50 are provided here in the front area. Since the free edges 44 of the guide elements 40 extend into the rotation range of the blade ends 28, they are offset radially outward in the rear area in order to reliably avoid contact with the blades. Of course, the edges can be offset accordingly throughout.

For all embodiments of the recirculation structure applies that the free edges 41 to 44 of the guide elements 37 to 40 need not be offset radially outward when the guide elements are made of a soft light metal or plastic, because a contact with the blade ends allowed 25 to 28 can be done without damaging the blades.

Claims (13)

1. A recirculation structure (1 to 4) for turbocompressors, having an annular chamber (29 to 32) arranged concentrically with the compressor axis in the area of the free blade ends (25 to 28) of a blade ring (15, 20, 23, 24), which annular chamber (29 to 32) radially adjoins the contour (11, 12) of the main flow channel (9, 10), or "annular space", the side of the annular chamber (29 to 32) adjoining the contour (11, 12) of the main flow channel (9, 10) being open over its axial length and over its entire circumference towards the main flow channel (9, 10), and having a plurality of guide elements (37 to 40) arranged in the annular chamber (29 to 32) and distributed over the circumference thereof, which guide elements (37 to 40) are so arranged and shaped that the recirculation flow enters in a manner favourable to flow in the axially rear area of the annular chamber (29 to 32) and the recirculation flow exits in the axially front area of the annular chamber (29 to 32) with a defined direction and optionally defined swirl relative to the downstream blade ring (15, 20, 23, 24), the guide elements (37 to 40) having recesses (45 to 50) in the front and/or rear area of the annular chamber (29 to 32) for flow passage in the circumferential direction, characterised in that the free edges (41 to 44) of the guide elements (37 to 40) lie over their axial length on or close to the contour (11, 12) of the main flow channel (9, 10) and in that the axial centre of the annular chamber (29 to 32) lies upstream of the axial centre of the free blade ends (25 to 28).
2. A recirculation structure according to claim 1, characterised in that it is arranged singly or multiply fixed to the casing, i.e. statically, in the area of one or more moving blade rings (20, 23, 24) and/or singly or multiply fixed to the hub, i.e. rotatingly, in the area of one or more guide blade rings (15).
3. A recirculation structure according to claim 1 or claim 2, characterised in that it is arranged in a single- or multi-stage turbocompressor of axial, diagonal or radial construction.
4. A recirculation structure according to any one of the preceding claims, characterised in that the axially front wall (33) and the axially rear wall (34) of the annular chamber (29) are inclined, starting from their edges (35, 36) at the contour (11) of the main flow channel (9), by the same or a different angle α upstream, i.e. obliquely forwards.
5. A recirculation structure according to claim 4, characterised in that the angle of inclination α of the axially front and axially rear walls of the annular chamber starting from the radial direction exhibits a value in the range of from 30° to 60°.
6. A recirculation structure according to any one of the preceding claims, characterised in that the guide elements (37 to 40) are constructed in the manner of sheet metal, flat or bent, with a constant thickness, or in the manner of blades, bent three-dimensionally, with varying thickness and with defined profile sections.
7. A recirculation structure according to any one of the preceding claims, characterised in that the guide elements (37 to 40), when viewed axially, are arranged radially, inclined in the circumferential direction or bent in the circumferential direction, wherein in the case of inclination or a bend, the angles β are so selected that entry of the recirculation flow into the annular chamber (29 to 32) is simplified fluidically, i.e. takes place in a manner favourable to flow.
8. A recirculation structure according to any one of the preceding claims, characterised in that the ratio of the total flow volume to the total volume of the guide elements (37 to 40) inside the recirculation structure (1 to 4) is selected to be as large as possible, i.e. the guide elements (37 to 40) are made as thin-walled or thinly profiled as possible.
9. A recirculation structure according to any one of the preceding claims, in which the guide elements (40) extend axially as far as into the area of the free blade ends (28), characterised in that the free edges (44) of the guide elements (40) are set back radially so far, at least in the area of the free blade ends (28), that in normal operation of the turbocompressor there is no contact between the blade ends (28) and the guide elements (40).
10. A recirculation structure according to any one of the preceding claims, characterised in that the guide elements (37 to 40) consist of a metal, such as steel or an Ni- or Co-based alloy, a light metal, such as Al, or a plastics material, such as thermoplastics, thermosetting plastics or elastomers.
11. A recirculation structure according to claim 10, characterised in that, in the case of light metal or plastics material, the free edges (41 to 44) of the guide elements (37 to 40) extend as far as into the area of the free blade ends (25 to 28) and contact is possible.
12. An aircraft engine, including a turbocompressor having at least one recirculation structure (1 to 4) according to one or more of the preceding claims.
13. A stationary gas turbine, including a turbocompressor having at least one recirculation structure (1 to 4) according to one or more of claims 1 to 11.

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